The present invention relates to transistors and integrated circuits, and more specifically to integrated circuits of double-diffused MOS transistors (DMOS transistors).
An H-bridge driver circuit for driving a DC motor in forward and reverse directions (as disclosed in Denshi Kairo Dai Jiten, chapter 52, page 407, published by Seibundoshinkosha) includes four MOS transistors Tr1, Tr2, Tr3 and Tr4. The first and third MOS transistors Tr1 and Tr2 are connected in series between a power supply (VDD) and a ground. The second and fourth MOS transistors Tr2 and Tr4 are also connected in series between the power supply and ground. A load which is a motor M1 is connected between a first branch point between Tr1 and Tr3 and a second branch point between Tr2 and Tr4. In the H-bridge circuit, the drains of Tr1 and Tr2 (which are called high-side switches) are connected together. As to Tr3 and Tr4 (low-side switches), the sources are connected together.
An IC structure of one conventional example contains two DMOS transistors with drains connected together, which can be used as the highside switches Tr1 and Tr2. In this semiconductor device, the first transistor Tr1 consisting of parallel small transistors is formed only in a first half of the chip, and the second transistor Tr2 also consisting of parallel small transistors is formed only in a second half. Therefore, when Tr1 is on, and Tr2 is off, thermal energy is produced only in the first half of the chip by an electric current, and the second half of the chip is not utilized at all.